A pharmaceutical company plans to close its facility in Kansas City by the end of June. Sanofi-Aventis LLC plans to layoff 337 in Jackson County, according to a Worker Adjustment and Retraining Notification filing posted online by the Missouri Department of Economic Development. The WARN Act requires employers to provide a 60-day notice in advance of covered mass layoffs. Sanofi-Aventis first announced the closure of the manufacturing facility in Kansas City back in 2009, noting the closing of the site will happen in phases.